The invention relates to carburetors for internal combustion engines in which the richness of the air-fuel mixture supplied to the engine is adjusted responsive to the composition of the engine exhaust gases.
The invention relates more particularly to carburetors for internal combustion engine comprising a float chamber and a device for adjusting the pressure in the tank to a value in dependence on the composition of the engine exhaust gases, the device comprising a source of pressure different from atmospheric pressure and a probe immersed in the exhaust gases and supplying a signal depending on the composition thereof.
In a prior art device of that type (U.S. Pat. No. 3,730,157) the pressure source is either a region at a pressure below atmospheric pressure or a pump supplying compressed air.
That prior art device can bring the pressure of the float chamber either to a value between atmospheric pressure and a subatmospheric pressure (which tends to reduce the amount of fuel admitted into the carburetor inlet pipe and consequently to reduce the richness of the air-fuel mixture supplied to the engine) or to a pressure between atmospheric pressure and the pressure supplied by the compressed air source. However, a single device cannot supply pressures above and below atmospheric pressure.
It is an object of the invention to provide a carburetor wherein the pressure may be adjusted with a wider range than in prior art carburetor, while it includes a single source of air at a pressure different from atmospheric pressure.
According to the invention, there is provided, inter alia, a carburetor for internal combustion engine, comprising a float chamber and a device for adjusting the gas pressure in the float chamber, said device having: a source of air at a pressure different from atmospheric pressure; airflow passage means connecting said source and atmosphere means on said airflow passage means for impressing a head loss to the airflow; an oxygen sensitive probe adapted to be immersed in the exhaust gas of the engine and to provide an electrical signal representative of the oxygen content of said exhaust gases; control means for actuating said throttle means responsive to said electrical signal; and means connected to the float chamber, located in the airflow passage means and so constructed that it conveys to the float chamber a pressure whose value is outside the range between the pressure of the source and atmospheric pressure for a predetermined range of values of said head loss.
The source can be at a pressure above atmospheric pressure and then the last-mentioned means typically comprises a construction, which may be the throat of a venturi.
Alternately, the source can be at a pressure below atmospheric pressure, for instance the vacuum downstream of the operator actuable throttle member of a carburetor; then the last named means can comprise a Pitot tube.
The head loss means may be a valve actuated in dependence on the signal supplied by the probe for adjusting the flow rate of air through the pipe.
The invention will be better understood from the following description of carburetors constituting non-limitative embodiments thereof.